1. Field of the Invention
The present invention relates to a guide roller unit coming into contact with printing paper. The present invention also relates to a printer incorporating such a guide roller unit.
2. Description of the Related Art
In an electrophotographic printer, long continuous printing paper is often used for making a hard copy of the output information. Without any particular needs, only one side of the printing paper is used for printing. To economize the printing paper or achieve high-speed printing operation, however, it is desirable that the both sides of the printing paper are used for printing.
In a printer designed to perform such double-side printing, the operation may generally proceed as follows. First, a toner image is produced on one side (first side) of the printing paper by a first printing unit. Then, a fixing unit fuses the toner image onto the paper for permanent fixation. The printing paper is then fed to a second printing unit located downstream from the first printing unit along the paper transfer path. There, another toner image is produced on the other side (second side) of the printing paper, and fused for permanent fixation. According to this process, the printing paper may be thermally damaged (shriveled, for example) when the toner image on the first side of the paper is fused. Unfavorably, the second printing unit may fail to produce a proper toner image on such deformed printing paper.
This problem can be addressed by the following procedure. To begin with, a first transfer unit causes a toner image produced on a first photosensitive drum to be transferred onto a first side of the printing paper. Then, a second transfer unit, disposed downstream from the first transfer unit, causes a toner image produced on a second photosensitive drum to be transferred onto a second side (the opposite side) of the printing paper. Finally, two fixing units, disposed further downstream along the paper transfer path, fuse the unfixed transferred toner images onto the first and second sides of the printing paper, respectively. According to this printing procedure, the fixing of the toner images is performed after the transferring of the toner images from the photosensitive drums to the printing paper. Thus, it is possible to prevent the deterioration of printing quality which would otherwise result from the thermally deformed printing paper.
While enjoying such an advantage, the above printing method suffers the following drawback.
For implementing the printing, one or two guide roller units need to be provided for maintaining a prescribed distance between the printing paper and the first or second photosensitive drum. The guide roller unit is provided with a guide roller coming into contact with the printing paper. While contacting with the printing paper, the guide roller is caused to roll over the unfused toner image transferred onto the paper, whereby some toner is adhered to the contact surface of the guide roller.
In order to keep the guide roller clean, the guide roller unit is provided with a cleaning blade held in contact with the contact surface of the guide roller for scraping off the adhered toner from the rotating roller. In this arrangement, however, paper dust or any other dust tends to get stuck between the cleaning blade and the contact surface of the guide roller, preventing the cleaning blade from coming into full contact with the guide roller. In this situation, the adhering toner on the guide roller cannot be scraped off completely, which deteriorates the printing quality.
The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a guide roller unit whereby a collection of paper dust (or any other dust) can be automatically shaken off the cleaning blade.
According to a first aspect of the present invention, there is provided a guide roller unit including: a guide roller for guiding printing paper, the guide roller being provided with a contact surface that comes into contact with a toner image forming surface of the printing paper; and a cleaning blade that comes into contact with the contact surface of the guide roller for removing toner adhered to the contact surface. The contact surface of the guide roller is provided with a blade contact portion for vibrating the cleaning blade so that a collection of dust can be shaken off the blade.
Preferably, the blade contact portion may be a projection or a groove. The projection may be about 20 xcexcm in height, while the groove may be about 20 xcexcm in depth.
Preferably, the guide roller may be composed of a core made of a stainless metal and a fluoroplastic layer surrounding the core.
Preferably, the blade contact portion, such as a projection and a groove, extends over the entire width of the contact surface of the guide roller.
According to a second aspect of the present invention, there is provided a printer including: a photosensitive member upon which a toner image is produced; a transfer unit for transferring the toner image onto a first surface of the printing paper; a fixing unit for fixing the transferred toner image on the first surface of the printing paper, the fixing unit being located downstream from the transfer unit along a paper transfer path for the printing paper; and a guide roller unit that includes a guide roller coming into contact with the first surface of the printing paper, the guide roller unit also including a cleaning blade coming into contact with the guide roller for removing toner adhering to the guide roller. The guide roller unit may be located between the transfer unit and the fixing unit. The guide roller is provided with at least one of a projection and a groove that extend along the rotational axis of the guide roller for vibrating the cleaning blade by contacting therewith.
Preferably, the printer of the present invention may further include a detecting unit for checking whether or not the guide roller is unacceptably worn thin.
Preferably, the detecting unit may monitor the variation in driving current supplied to a motor to actuate the guide roller.
Preferably, the printer of the present invention may further include: an additional photosensitive-member; an additional transfer unit for causing a toner image produced on the additional photosensitive member to be transferred onto a second surface of the printing paper opposite to the first surface of the printing paper; a first fixing unit for fixing the toner image transferred onto the first surface, the first fixing unit being located downstream from the additional transfer unit along the paper transfer path; and a second fixing unit for fixing the toner image transferred onto the second surface, the second fixing unit being located downstream from the additional transfer unit along the paper transfer path.
Preferably, the printer of the present invention may further include an additional guide roller unit located between the additional transfer unit and the second fixing unit. The additional guide roller unit may include a second-surface guide roller coming into contact with the second surface of the printing paper and also include a cleaning blade coming into contact with the second-surface guide roller for removing toner adhering to the second-surface guide roller. The second-surface guide roller is provided with one of a projection and a groove that come into contact with the cleaning blade.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.